The present invention relates to catheters for use in the medical arts, and more particularly relates to such catheters having strengthening filaments associated therewith.
There are a number of medical procedures which are currently carried out by the use of a catheter which can be inserted into a body cavity or blood vessel of a patient. Such catheters include catheters for the localized delivery of diagnostic or therapeutic agents, catheters including one or more inflatable balloons for performing an angioplasty or similar occlusion clearing procedure, and catheters for the infusion of diagnostic or therapeutic agents over a specified region within a patient's body, as well as combinations of these catheters and others. Catheters for such medical uses are normally constructed from polymeric materials such as nylon, polyurethane, polyether polyamide blends, and other such materials. These materials provide flexibility and softness which helps to prevent damage to the patient's vessels which the catheter must traverse.
In many cases, catheters must be passed through a relatively tortious pathway such as a series of blood vessels within the patient's body so that the catheter can perform the desired function. It is therefore often desirable to have a catheter with a high degree of torquability along its length while maintaining the high degree of flexibility. One way of providing a catheter which the desired torquability is to include a reinforcing filament within the walls of the catheter.
Catheters having a reinforcing filament are known in the prior art, as shown in FIGS. 1 and 2. In particular, FIG. 1 is a plan view of a portion of a catheter, generally designated by reference numeral 10, having a number of reinforcing filaments, two of which are identified by reference numerals 20, 25. FIG. 2 is a cross sectional view of filaments 20, 25, taken at the location where the filaments 20, 25, cross each other.
Catheters may be provided with reinforcing filaments according to any one of a number of known methods. For example, in one method, an assembly of multiple spools of filament material are provided at equally spaced points around the periphery of a circular plane. This assembly is provided surrounding the exit of a standard tube extrusion machine so that the filaments may be provided during the production of the catheter. As the catheter is extruded, the assembly rotates such that a first set of spools of material provide equal and parallel spaced filaments to the catheter in a clockwise, barber pole fashion along the length of the catheter, and a second set of spools of material provide equal and parallel spaced filaments to the catheter in a counterclockwise, barber pole fashion along the length of the catheter. The first set of spools alternates with the second set of spools so that the filaments running in opposite directions cross over and under one another to form a braid pattern.
The number of spools in each set; i.e. clockwise and counterclockwise, may vary depending on the amount of reinforcing filament is desired to be incorporated within the catheter. In particular, the total number of spools may range from two to greater than fifty six. Normally, equal numbers of spools will be used for each set; i.e. clockwise and counterclockwise. However, different numbers of spools may also be used.
In a particular example, the catheter 10, is provided with the reinforcing filaments using an assembly of sixteen spools of filament material which are provided at sixteen equally spaced points around the periphery of a circular plane. As the catheter is extruded, the assembly rotates such that a first set of eight spools of material provide eight equal and parallel spaced filaments to the catheter in a clockwise, barber pole fashion along the length of the catheter, and a second set of eight spools of material provide eight equal and parallel spaced filaments to the catheter in a counterclockwise, barber pole fashion along the length of the catheter. The first set of eight spools alternates with the second set of eight spools so that the filaments running in opposite directions cross over and under one another to form the braid pattern as shown in part by FIG. 1.
The method described above places the reinforcing filaments continuously between a base coat extrusion and a top coat extrusion of the catheter. In an alternative to the above, a reel-to-reel process may be used. In this process, the base coat of the catheter is first extruded onto a mandril, the mandril being spooled off a first reel, coated with the base coat, and then spooled onto a second reel (thus the term "reel-to-reel"). Next, the reinforcing filaments are provided to the base coat in a separate reel-to-reel process using an assembly for the spools of reinforcing filaments similar to that described above. Finally, the base coat with reinforced filaments is provided with an extruded top coat using a third reel-to-reel process.
Another method of providing the reinforced filaments is to produce the catheter and the reinforced filament pattern; such as a braid, separately and then establish the filament pattern within the catheter through a series of hot die sizing processes.
Regardless of the method used, the filaments, such as filaments 20, 25, provided to the prior art catheter 10, help to increase the torquability of the catheter 10, but also allow the catheter 10, to remain relatively flexible. However, the filaments, such as filaments 20, 25, used in the prior art have a relatively large diameter, which requires the catheter 10, to have a greater wall thickness to fully surround the filaments 20, 25. The increased wall thickness; (i.e. the combination of base and top coats), increases the overall profile of the catheter 10. This means that the delivery rate capabilities of the catheter 10, will be compromised. In particular, a change of 0.002" to the inside diameter of a five french catheter can change the pressure required to deliver a specific flow of material to be delivered by as much as twenty five percent.
As noted above, the filaments, such as filaments 20, 25, are typically aligned in parallel fashion, to provide the braid pattern shown in FIG. 1. The braid pattern or density may be varied to achieve different torque characteristics and to alter the flexibility of the catheter. In particular, the denser the braid pattern, the greater the torque and the flexibility. The diameter of individual filaments, such as filaments 20, 25, are generally in the range of 0.002 to 0.004 inches and result in a catheter wall thickness in the range of 0.012 to 0.015 inches.
There remains a need in the art for improvements to braided catheters.